Sciencemadness Discussion Board

How to make white fuming nitric acid from red fuming for rdx synthesis

nitropyrotech - 27-5-2025 at 11:59

Hello, anyone know how to make white fuming nitric acid from red fuming with NOx gases dissolved in it, I tried to do it with 35% hydrogen peroxide but it ended in an runaway reaction where I got to breathe the beutiful NOx gases in, even when the nitric acid was cooled down in a freezer before. So are there any other methods, that would work, I heard that blasting air into the acid will get the NOx gases away and the yellowish color too, I just need white fuming nitric acid for synthesis of rdx because I just got a shit yield (from 10g hexamine I got 2g RDX), I used regular RFNA and the modified bachmann route where I added Ammonium nitrate first to the RFNA and than slowly start to add the hexamine, after all the additioin everything was stabilized at room temp while stirring for 30 min first and than heated to 80C and kept stirring for 30min, after recrystallisation I got 2g of RDX from hexamine, I dont know the ratios of acetic anhydride and I cant find literatures online so I just went without it, would be helpful if anyone know the ratios, acetic anhydride is pretty diffculft to obtain and its pretty expensive for me because I live in germany so I would appreciate a method that use less of this stuff as possible

Sir_Gawain - 27-5-2025 at 13:38

The hydrogen peroxide method works great for me, perhaps you added too much. For the RDX synthesis, I’ve had much better luck by first making hexamine dinitrate, then reacting that with WFNA. 68% nitric acid is used to make the HDN so you save on WFNA. The reports of HDN’s hygroscopicity are overstated imo, I found it dries quite easily. I’ve even stored some in a poorly sealed bottle for over a year with little decomposition.

greenlight - 28-5-2025 at 09:05

Second that, much better to go hexamine dinitrate first and then to RDX.

As for the dry air method, I have used it many times with success. Warmed, stirred red fuming nitric acid in a beaker on a hotplate stirrer with air bubbled in from an aquarium pump inside a desiccator covered with fresh calcium chloride granules results in clear colourless acid every time. Do this with proper ventilation outside of course.

[Edited on 28-5-2025 by greenlight]

ManyInterests - 28-5-2025 at 14:59

Quote: Originally posted by Sir_Gawain  
The hydrogen peroxide method works great for me, perhaps you added too much. For the RDX synthesis, I’ve had much better luck by first making hexamine dinitrate, then reacting that with WFNA. 68% nitric acid is used to make the HDN so you save on WFNA. The reports of HDN’s hygroscopicity are overstated imo, I found it dries quite easily. I’ve even stored some in a poorly sealed bottle for over a year with little decomposition.


My HDN felt quite moist even if I stored it in a tightly wrapped plastic bag in a sealed plastic tupperware for a long time (and I had dried it previously). I got so frustrated with HDN that I burned my supply and I want to use straight hexamine going forward. This is even though hexmaine MIGHT be mildly hygroscopic.

I tried to do an RDX synthesis recently, but it failed and ended in a runaway. Thankfully I prepared well beforehand and had a large bucket of cold water to dump everything in. But I think in this situation it was a case of very poorly made WFNA (which I am sure at this point wasn't WFNA).

I wanted to talk about that. Since that attempt at making WFNA was my first attempt at doing a reflux distillation. What I did is I made 500ml of 83% nitric acid using sodium nitrate and I redistilled it with 500ml of sulfuric acid. I think I messed up that redistillation and accidentally got sulfuric acid in my stuff (I had a final yield of 355ml before stopping).

The reason why I think I had gotten sulfuric acid is because the SG of my end result was over 1.55g. This is impossible. and it was fuming red throughout. Adding the ammonium nitrate didn't dissolve and it just didn't work correctly. When I cooled it down and started adding my HDN, there were red fumes of NO2 throughout even if it wasn't a runaway.

One thing is that I did not end up with any RDX at all. In previous attempts I did have a runaway (or near runaway) before dumping, and I did get some RDX (that I later dissolved in azeotropic nitric acid for purification). This tells me I seriously screwed up making WFNA with a redistillation.

One issue I had with redistilling is that I broke the only thermometer adapters that could fit in my flask. I replacements and of other thermometer adapters of various lengths so hopefully I will have multiple ways to read my temperature next time. I really, really want to succeed at getting good yields of RDX.

Sir_Gawain - 28-5-2025 at 15:32

Did you rinse the HDN with a little ice cold acetone and dry thoroughly on the pump?

bariumbromate - 28-5-2025 at 18:50

simply add a half gram of Urea to every 500ml of nitric acid that works fine just add very slowly to avoid a runaway reaction

ManyInterests - 29-5-2025 at 01:51

Quote: Originally posted by Sir_Gawain  
Did you rinse the HDN with a little ice cold acetone and dry thoroughly on the pump?


Room temperature acetone, and yes I did.

nitropyrotech - 30-5-2025 at 03:24

Quote: Originally posted by Sir_Gawain  
The hydrogen peroxide method works great for me, perhaps you added too much. For the RDX synthesis, I’ve had much better luck by first making hexamine dinitrate, then reacting that with WFNA. 68% nitric acid is used to make the HDN so you save on WFNA. The reports of HDN’s hygroscopicity are overstated imo, I found it dries quite easily. I’ve even stored some in a poorly sealed bottle for over a year with little decomposition.

I have never tried the method with hexamine dinitrate before, Ive heard it improves thermal stability so it wont take 2 hours to add everything but I think I ll try the hexamine dinitrate route and see how it will go, I also hope it will improve my yield without use of acetic anhydride

nitropyrotech - 30-5-2025 at 03:28

Quote: Originally posted by greenlight  
Second that, much better to go hexamine dinitrate first and then to RDX.

As for the dry air method, I have used it many times with success. Warmed, stirred red fuming nitric acid in a beaker on a hotplate stirrer with air bubbled in from an aquarium pump inside a desiccator covered with fresh calcium chloride granules results in clear colourless acid every time. Do this with proper ventilation outside of course.

[Edited on 28-5-2025 by greenlight]

Will it also work when I put a tube inside of the RFNA and just blast air from a aquarium pump into it because I dont have a dessicator

nitropyrotech - 30-5-2025 at 03:28

Quote: Originally posted by greenlight  
Second that, much better to go hexamine dinitrate first and then to RDX.

As for the dry air method, I have used it many times with success. Warmed, stirred red fuming nitric acid in a beaker on a hotplate stirrer with air bubbled in from an aquarium pump inside a desiccator covered with fresh calcium chloride granules results in clear colourless acid every time. Do this with proper ventilation outside of course.

[Edited on 28-5-2025 by greenlight]

Will it also work when I put a tube inside of the RFNA and just blast air from a aquarium pump into it because I dont have a dessicator

greenlight - 30-5-2025 at 19:25

Quote: Originally posted by nitropyrotech  
Quote: Originally posted by greenlight  
Second that, much better to go hexamine dinitrate first and then to RDX.

As for the dry air method, I have used it many times with success. Warmed, stirred red fuming nitric acid in a beaker on a hotplate stirrer with air bubbled in from an aquarium pump inside a desiccator covered with fresh calcium chloride granules results in clear colourless acid every time. Do this with proper ventilation outside of course.

[Edited on 28-5-2025 by greenlight]

Will it also work when I put a tube inside of the RFNA and just blast air from a aquarium pump into it because I dont have a dessicator


Ideally, the air need to dry and free of any water vapour. dDpending on the ambient weather conditions, you could introduce further water into your acid diluting it.
You don't have to have a desiccator, just run you aquarium pump covered in damp rid or other similar hygroscopic drying agent inside any plastic container it fits.

FrankRizzo - 31-5-2025 at 10:04

It's trivial to make an inline dessicator with a soda bottle or similar, filled with indicating silica gel or damp rid.

nitropyrotech - 6-6-2025 at 07:20

Quote: Originally posted by greenlight  
Quote: Originally posted by nitropyrotech  
Quote: Originally posted by greenlight  
Second that, much better to go hexamine dinitrate first and then to RDX.

As for the dry air method, I have used it many times with success. Warmed, stirred red fuming nitric acid in a beaker on a hotplate stirrer with air bubbled in from an aquarium pump inside a desiccator covered with fresh calcium chloride granules results in clear colourless acid every time. Do this with proper ventilation outside of course.

You think Ammoniumnitrate will work too? I mean I have bulk ordered it and have 300kg at home

[Edited on 28-5-2025 by greenlight]

Will it also work when I put a tube inside of the RFNA and just blast air from a aquarium pump into it because I dont have a dessicator


Ideally, the air need to dry and free of any water vapour. dDpending on the ambient weather conditions, you could introduce further water into your acid diluting it.
You don't have to have a desiccator, just run you aquarium pump covered in damp rid or other similar hygroscopic drying agent inside any plastic container it fits.

nitropyrotech - 6-6-2025 at 07:23

Quote: Originally posted by greenlight  
Quote: Originally posted by nitropyrotech  
Quote: Originally posted by greenlight  
Second that, much better to go hexamine dinitrate first and then to RDX.

As for the dry air method, I have used it many times with success. Warmed, stirred red fuming nitric acid in a beaker on a hotplate stirrer with air bubbled in from an aquarium pump inside a desiccator covered with fresh calcium chloride granules results in clear colourless acid every time. Do this with proper ventilation outside of course.



[Edited on 28-5-2025 by greenlight]

Will it also work when I put a tube inside of the RFNA and just blast air from a aquarium pump into it because I dont have a dessicator


Ideally, the air need to dry and free of any water vapour. dDpending on the ambient weather conditions, you could introduce further water into your acid diluting it.
You don't have to have a desiccator, just run you aquarium pump covered in damp rid or other similar hygroscopic drying agent inside any plastic container it fits.

Ammoniumnitrate will it work too I bulk orderd 300kg from my supplier from latvia

ManyInterests - 24-6-2025 at 11:49

Quote:
Ammoniumnitrate will it work too I bulk orderd 300kg from my supplier from latvia


300 kg? Wow, that's dedication!

But for me right now I am trying an RDX synthesis with pure hexamine and no HDN. My usual method but holy hell are the additions HOT. I had to put my cooling bath and the beaker in the freezer once for 90 minutes before resuming, and right now the former solid ice block has melted almost completely (but no runaway and I stirred for 8.5 minutes before covering and putting it back in the freezer) when the nitration beaker was at 14.5C. I will wait another 3 hours or so before everything cools... and I only added a little bit of the hexamine in comparison to how much I am making.

Man this stuff is a bitch to make. I want to make a decent amount just as a challenge.

Edit: I have a question: Since I have had runaways with RDX in the past and many failures with making it (leading to very poor yields salvaged from crashing the acid to prevent a disaster) Would a multi-day process work? Like there is no way I can add all the stuff to my mixture in one day. It will take far too long. I've done many nitrations before, and normally I would just do the whole thing from nitrating to crashing it and then filtering/washing it in one session, but I simply cannot do this with RDX due to the extreme heat it produces in hexamine additions. HDN is a little less hot, I know, but even HDN doesn't mitigate the heat that much.

so it makes me wonder... just how bad for the yield would it be to take that many breaks between additions to cool back down in the freezer?

[Edited on 24-6-2025 by ManyInterests]

Microtek - 24-6-2025 at 13:47

It sounds strange to me that you are getting that much of an exotherm. When I do it, the exotherm is quite manageable. I sounds as if your ice bath is actually just a block of ice, is that the case? If so, you should take the advice we gave you before and replace it with a proper liquid bath, preferably stirred. The heat transfer from forced convection is much greater that what you will get from a static block.

Also, have you tried adding two molar equivalents (relative to hexamine) of dried AN to the HNO3 before adding the hexamine? It increases the yield and also, in my experience, makes it more well behaved. The only downside is that drying AN is not as trivial an operation as it may seem. 50 C for 18 hours has been used by Bachmann, IIRC.

[Edited on 24-6-2025 by Microtek]

ManyInterests - 24-6-2025 at 17:16

Quote: Originally posted by Microtek  
It sounds strange to me that you are getting that much of an exotherm. When I do it, the exotherm is quite manageable. I sounds as if your ice bath is actually just a block of ice, is that the case? If so, you should take the advice we gave you before and replace it with a proper liquid bath, preferably stirred. The heat transfer from forced convection is much greater that what you will get from a static block.

Also, have you tried adding two molar equivalents (relative to hexamine) of dried AN to the HNO3 before adding the hexamine? It increases the yield and also, in my experience, makes it more well behaved. The only downside is that drying AN is not as trivial an operation as it may seem. 50 C for 18 hours has been used by Bachmann, IIRC.

[Edited on 24-6-2025 by Microtek]


Yes and Yes.

Ok I didn't dry the AN that much, I wasn't aware it would take that much to dry it...

So here is what happened. I first made around 515ml of 99% (1.51 SG) nitric acid. I am proud that I got that much in one day (I did no less than 4 distillations with 2 liter flasks). It red with NO2, but after leaving it in the freezer (loosely closed cap and in a bag full of sodium bicarbonate) for 48 hours it got a little better. I added the AN and some urea with stirring for 30 minutes to allow NO2 to escape and for it to clear up a bit. It was still a bit red, but that couldn't have affected it that much, could it?

BTW, This time I did today was the SECOND time I did it using AN... but, just like the first time I had done earlier. It was a disaster! No joke! Despite controlled additions, my final addition (which was larger than previous, I must admit) produced a runaway, so I had to crash it to avoid a disaster. I had some very mild NO2 inhalation, but nothing serious. No RDX came out in solution, like the previous time.

So right now I am baffled as all hell. I worked REALLY hard to make that much nitric acid, and while I can do that again easily, it was a lot of work and I don't want to have to do this again and still fail. BTW, I had measured out 170g of hexamine and barely 20g was added over a span of 9 hours at least. There was NO2 gas coming out throughout, BTW. The 2 times I did it with AN added in the nitric acid and I still had it fail. Doing it with HDN won't do any better since that is what I did last time.

I am legit baffled as to what I am doing wrong?

For the ice bath, what I did is made a salt water solution, put the beaker in the middle, then put the whole thing in the freezer (covered obviously). until everything froze solid, around 6 or 8 hours. it was really, really cold. But despite this, in my first addition, the iceblock almost completely melted in an hour of addition. This shit was HOT.

I thought the AN and urea (around 1g, not much) was supposed to stop runaways like this from happening? Or at least cool down the reaction?

I did do RDX two times prior without the use of AN or urea, I wasn't sure how red it was back then, but in the end I had a runaway on one of them (but it did not resemble these at all, there was no fizzing and no foaming, but the temperature was rising steadily and uncontrollably, so I had to crash it. Despite that, I had a 50% yield of RDX from the amount of HDN I put in. The first time I also had a similar yield. But in these cases I had no yield.

I know I am using increasing amounts of reagents... but that is just how I work. I always keep making things bigger... and also I want to succeed! RDX is pissing me off. I made almost everything else on my bucket list of energetics, but RDX has been an absolute bitch to make so far and it is pissing me off.

Edit: I am just going to make RDX with plain nitric acid and no AN going forward. Since know I know it doesn't HAVE to be 99%, I can bubble air through the acid first while heating to clear out the NO2, not necessarily super dry air, but if I get 99% acid again, it'll still work with 95% just fine. Also one reason why I added the AN is to make the heating step safer since I did hear that it also eliminated any risk of an accidental detonation. What I will do is after the addition is all done I will only gently heat it (using a hot water bath) to 50C before dumping, there isn't much risk in that. To remove any impurities what I can do is simply redissolve the RDX later in 50-60% nitric acid and heat it that way. I did it before, no risk of danger. The yield will still be not good, around 50% of the beginning material or so... but 50% is better than nothing.

[Edited on 25-6-2025 by ManyInterests]

Microtek - 24-6-2025 at 23:29

OK, I am almost certain that the NOx in your nitric is to blame for the excessive exotherm. NO2 (red/brown) is in an equilibrium with N2O4 (almost colorless) and that equilibrium is displaced far towards the N2O4 side of the reaction at low temp. This means that when you see the colour fade when you put the nitric in the freezer, it doesn't mean that the NOx disappears. It is still there in the form of N2O4 and will oxidize the hexamine fragments and produce a lot of heat while also lowering your yields.
Purging the nitric at ca. 50 C with dried air is the way to go. You can just make a lidded jar with two tubes, one reaching to the bottom and one only just going through the lid. Fill it with a drying agent such as CaCl2 (flake preferably) or silica gel, and use an aquarium pump to blow air through it and into your nitric. A good bubbler can be made by making many piercings in the bulb of a single use plastic pipette.

The airstream will volatilize some of your nitric, so if you set up for reflux you will save some of that and also reduce the fumes.

ManyInterests - 24-6-2025 at 23:50

Quote: Originally posted by Microtek  
OK, I am almost certain that the NOx in your nitric is to blame for the excessive exotherm. NO2 (red/brown) is in an equilibrium with N2O4 (almost colorless) and that equilibrium is displaced far towards the N2O4 side of the reaction at low temp. This means that when you see the colour fade when you put the nitric in the freezer, it doesn't mean that the NOx disappears. It is still there in the form of N2O4 and will oxidize the hexamine fragments and produce a lot of heat while also lowering your yields.
Purging the nitric at ca. 50 C with dried air is the way to go. You can just make a lidded jar with two tubes, one reaching to the bottom and one only just going through the lid. Fill it with a drying agent such as CaCl2 (flake preferably) or silica gel, and use an aquarium pump to blow air through it and into your nitric. A good bubbler can be made by making many piercings in the bulb of a single use plastic pipette.

The airstream will volatilize some of your nitric, so if you set up for reflux you will save some of that and also reduce the fumes.


I believe you. I knew that people say that the nitric shouldn't be red, but I had no idea it would have that big of an outsized effect. Especially since when I did do RDX without AN I am seriously questioning if if it was that red.

At any rate the next time I do this I will run a much smaller batch so that way if something goes wrong I won't lose a lot of basic reagents. I also learned that using bisulfate to make nitric acid needs more specialized care, since I ended up losing two flasks. Making this the most expensive experiment I ever ran.

I formerly used small inflatable pump, but I think I can spare the money for a quieter aquarium pump, since I did find some that are cheap and effective.

For the setup. I can make it work, but I am not sure how to set it up for reflux. Previously when I did it, I did have a gas wash bottle filled with CaCl2 (not flaked, they're spheres, however) but the end went directly to a beaker. I don't mind losing some nitric as long as I rid my HNO3 of the stuff.

I want to succeed!

Edit: Would putting the pump itself in CaCl2 also help to dry the air some more?

[Edited on 25-6-2025 by ManyInterests]

Microtek - 25-6-2025 at 01:24

CaCl2 spheres are fine. When I said "preferably flakes", I just meant that it shouldn't be powdered, as that will clog up and make a mess. It is not critical what kind of air pump you are using, but the airflow shouldn't be too fast, or the CaCl2 won't have time to dehydrate the airstream.

Setting up for reflux is similar to a distillation setup, but the condensed liquid runs back into the boiling flask. It is usually done simply by inserting the condenser directly, and vertically, into the boiling flask. It is not necessary to do this, but it will reduce the amount of HNO3 vapours in your lab. I find that these fumes are quite hard on my fume hood extraction fans.

ManyInterests - 25-6-2025 at 15:51

Quote: Originally posted by Microtek  
CaCl2 spheres are fine. When I said "preferably flakes", I just meant that it shouldn't be powdered, as that will clog up and make a mess. It is not critical what kind of air pump you are using, but the airflow shouldn't be too fast, or the CaCl2 won't have time to dehydrate the airstream.

Setting up for reflux is similar to a distillation setup, but the condensed liquid runs back into the boiling flask. It is usually done simply by inserting the condenser directly, and vertically, into the boiling flask. It is not necessary to do this, but it will reduce the amount of HNO3 vapours in your lab. I find that these fumes are quite hard on my fume hood extraction fans.


I can manage with that.

Oh and I forgot to mention something important. As I said, with my two RDX synthesis, the first one using redistilled nitric acid.

It was my first time concentrating RFNA (83%) into WFNA. But I am not sure if I succeeded. I ran into some problems. While setting up my distillation apparatus I accidentally broke my thermoprobe. I have since replaced it and got other ones of smaller length, allowing me to fit it in a reflux setup.

But at that time I couldn't... meaning I had to play it all by ear. I put in a 1:1 ratio of sulfuric acid to my nitric acid. Again, I had no idea how hot it was being, and I tried to turn the apparatus on and off as needed. But I cannot be sure if all the nitric distilled over or it got so hot that some sulfuric got over. I just wasn't sure. It was my first time doing it.

I am pretty sure something was very off about the end batch. Because A: its SG was 1.57, which is impossible unless there were contaminants in it, and B: It was fuming red throughout at all times. I can't be sure if I had some sulfuric acid come over or what.

But whatever it was, it had the same result of my 2nd batch, except even worse. I am not sure if even the ammonium nitrate fully dissolved in the thing.

I ordered some magnesium nitrate (500g) from onxymet and it is currently on its way, I also have the new thermoadapters that are GREAT which worked well for my previous distillations to make decent 99% acid.

I know Nurdrage has a video on using magnesium nitrate to concentrate azeotropic to WFNA territory... but have you done it before? And how to salvage my magnesium nitrate for reuse and remove any left over nitric acid from it?

BoroNar - 7-1-2026 at 12:19

on the same matter here, cannot get green-yellow color out of nitric acid, redistilled two times over sulfuric(96%) (1:1) but yellow color is still present. Both dist over aspirator vacuum, temp at head 32c max, liquid in flask about 50-60c. Concentration is near 100% as my density meter can be trusted.

Tried bubbling air using fish tank pump, with inline silica gel dessicator tube. Also tried commercial O2 wlders use. Both bubbling about 1 hour, with stirrer and nice bubbler tube. Tried to warm up a bit while bubbling but it made things worse, got reddish. In freezer acid gets a bit clear.

I can't think what else I am missing, maybe ozone? Friend has generator. Urea will dillute, H2O2 max I can get is 15% and don't want to dillute so precious, almost anhydrous... already lost many during distills.

any help would be appreciated

ManyInterests - 7-1-2026 at 14:01

Quote: Originally posted by BoroNar  
on the same matter here, cannot get green-yellow color out of nitric acid, redistilled two times over sulfuric(96%) (1:1) but yellow color is still present. Both dist over aspirator vacuum, temp at head 32c max, liquid in flask about 50-60c. Concentration is near 100% as my density meter can be trusted.

Tried bubbling air using fish tank pump, with inline silica gel dessicator tube. Also tried commercial O2 wlders use. Both bubbling about 1 hour, with stirrer and nice bubbler tube. Tried to warm up a bit while bubbling but it made things worse, got reddish. In freezer acid gets a bit clear.

I can't think what else I am missing, maybe ozone? Friend has generator. Urea will dillute, H2O2 max I can get is 15% and don't want to dillute so precious, almost anhydrous... already lost many during distills.

any help would be appreciated


You'll need an NO2 scrubber. H2O2 I find is not ideal, a little urea (finely powdered) added will help, try adding 0.5g at a time, with a little heat and strong stirring/bubbling it should clear up. it did for me.

It also does take a bit of time for it work, it took me a lot longer than 1 hour for it to clear up, but my concentration was 95%. BTW 100% nitric acid is basically impossible in a home lab. I was able to get 99% once, but it has some mild NO2 contamination.

BoroNar - 8-1-2026 at 03:04

ManyInterests

Thanks,
I have option to dist some high concentration H2O2 from 15% but it is not easy and additional work.
When I bubbled for one hour, it also decreased in concentration, but I think heating produced more NO2 and so no noticeable color change.
What temperature is recommended for urea reaction?

Could you share more info about NO2 scrubber? I can't have column that industry uses, but have scrubber glass tube producing tiny bubles from sand covered end. I can borrow U-shaped gas scrubber, will it be better be suited?


[Edited on 8-1-2026 by BoroNar]

ManyInterests - 8-1-2026 at 17:01

The scrubber I was referring to was urea. A simple addition of small quantities of powdered urea.

the way how I did it is add a little urea (0.5g at a time), heat it to around 40C (I didn't measure exactly) and with mild stirring and bubbling (like you, I have an aquarium pump) and just pump air through it with stirring. I let it cool down and reheat as many times as needed as it allows me to monitor the color. It always lightens up a little every time I do it. I can take a few hours to do, but it always worked like for me. I don't have any special equipment for it beyond that. Just a beaker and hotplate stirrer and the pump with glass straws.

ManyInterests - 14-1-2026 at 17:46

OK, so I need to post my latest result that I find very frustrating with RDX synth, especially since what I am supposed to get (or I think I'm supposed to get).

So I started with 250g or 263g of nitric acid (not entirely sure) the total amount was around 95% nitric acid that has been 100% purged of all NO2 (it was fully clear, no yellowness or red). I added to this 34.9g of anhydrous ammonium nitrate that I dried for over 24 hours at 90C in the oven, and I cooled it down to -5C and I added 30.5g of hexamine over the course of 4 hours and never allowed the temperature to rise over 5 or 6C. I then allowed it to reach room temperature (around 19C) slowly, I then started to heat it slowly with strong stirring throughout. I did hear fizzing coming from the solution, and fuming started around 50-60C, I continued to heat it until 80C, but I decided not to hold it for 30 minutes as it took me a very long to get it to that temperature, it emmitted a lot of fumes but I was able to handle it and there was a LOT of fizzing. I let it cool down slowly before putting it on a salt-water ice bath to let it get down to 0C before I dumped it.

My weird from 30.5g of hexamine was... 13.5g of RDX. It is the lowest yield I got. The last time I did RDX I used the same method (Knoffler if I am not mistaken) and I got almost the same amount of RDX as I put in in hexamine, but I did have a runaway at the 60C mark and saw red fumes, but I quickly dumped my beaker in the bucket and stopped the reaction. I wondered if the heating step is needed to go up to 80C or is something like 50C sufficient? Did I vaporize or destroy my RDX in addition to the other impurities?

I am confused here. RDX is by far the most difficult challenge of any energetic. Much more so than any other. So much time to get the nitric acid ready and it is all just... bleh.

greenlight - 14-1-2026 at 22:40

In literature, that manufacturing process is held at 55°C. Your lucky you didnt have a runaway reaction. That temperature seems outright dangerous to heat a nitrolysis reaction (or any nitration other than a C-nitration to). You are providing high kinetic energy to molecules within a "soup" of an acidified already sensitive compound. I would recommend never going that high again.

The fizzing to me definitely indicates possible side reactions or decomposition of your desired compound. You used colourless fuming nitric acid with minimal dissolved nitrogen dioxide so something is being decomposed into gas rapidly at that temperature.
It would have been more effective and safer heating at 50 for an extended period.

I recommend the Bachmann process where you first use azeotropic nitric acid to synthesise hexamine dinitrate and then performing a nitrolysis on that with the same reagents you used for this and a lower temperature. You already have half the nitro groups attached in the case of HDN, with less work to do in the final nitrolysis resulting in better yields and a smoother reaction at only moderate temperature.
The HDN is an extremely easy nitration and high yielding too.
If you try this method you will be amazed at the difference.

Alkoholvergiftung - 15-1-2026 at 00:05

Dug sayed in his video for the koffler reaction you need 80C. With lower temperatures the reaction with the NH4NO3 doesnt take place. Dont know if this is true but he looks like an serios source.

greenlight - 15-1-2026 at 03:11

My mistake, you are correct, sorry guys.
I was looking at the reaction scheme for synthesis from only hexamine and excess concentrated nitric acid.
The Koffler process does use temperature of 80°C. It seems it does not follow the traditional nitrolysis pathway where a heat value like that would result in a runaway.







[Edited on 15-1-2026 by greenlight]

greenlight - 15-1-2026 at 03:19

Found this thread discussing the temperature control and duration for the K process:

http://www.sciencemadness.org/talk/viewthread.php?tid=159924

The fuming can be expected from high purity nitric acid but I still believe the fizzing indicates decomposition occurring.
Maybe an attempt at a slightly lower temperature for a longer duration before the onset of the fizzing would run better?

ManyInterests - 15-1-2026 at 20:22

Quote: Originally posted by greenlight  
Found this thread discussing the temperature control and duration for the K process:

http://www.sciencemadness.org/talk/viewthread.php?tid=159924

The fuming can be expected from high purity nitric acid but I still believe the fizzing indicates decomposition occurring.
Maybe an attempt at a slightly lower temperature for a longer duration before the onset of the fizzing would run better?



I am glad to learn that the fizzing was not unique to my experience, and I think what happened is that a lot of my RDX decomposed by the heat. When I did this the first time (with clean nitric acid and no runaway during addition... a first) I did have a runaway at the 65C mark, but that is probably because I heated it too fast. However when I recovered the RDX it was around 30.5g from 29.5g starting hexamine. While there might be some mild impurities I don't think there is enough to impact performance and long-term storage that much, and also it was heated somewhat.

I did read in other literature and videos that heating to 50C is acceptable and sufficient. This is what I will do next time.

BoroNar - 28-1-2026 at 08:36

I've been scrubbing my RFNA for 2.5 days! Yes, about 36hours. Result is same as with dist over sulfuric acid. Slight yellow color is still present. Seems other approach is needed, fish bubbler route is not effective, thus have lost 20ml (about 10%) to Bicarb scrubber.

It seems more effort is needed to become member of WFNA makers club.

As far as I understand, one must work in a way not to have NO2 released first place, if once introduced in solution, becomes hard to evict.
What are options? What is the sure way to have clear nitric acid instead of red-green-yellow thing?

Always have Sulfuric Acid pre-cooled in freezer
Add KNO3 (dried to death, in hot oven @150deg for many hours) while stirring so no hotspot ever forms, no chance of premature release for NO2
use aspirator vacuum
and above all, use minimal temperature like 40deg or so and wait forever to distill tiny 200ml. Low dist temp also implies incomplete extraction of acid.

Will try described procedure, does anybody have practical hands on experience to give further advice and recommendation?

BoroNar - 17-2-2026 at 21:59

It seems clearing up RFNA is best done with ozone generator. Even some cheap unit I had access to worked, bubbling for just 1.5 hour was enough to clean 200ml RFNA.

But stuck to next problem with RDX, same thing as you guys here, K-method produces NO2 at 65c.
Process I am following is from Dug's video, exactly step-by-step, no even miniscule changes.
Tried two times and yes, temperature increase was slow and gradual.

May be impurities come from hexamine? it is from fuel tablets, recrystalized from water, filtered few times with different mesh filters (0.1um PTFE was the last) dried at low temp under vacuum.

Result was bit more than input hexamine, maybe it is good for first time but how to get that 2 mole result?

Microtek - 17-2-2026 at 23:31

In Urbanski's desription of the K-method, 1000 kg cyclonite requires 480-500 kg hexamine. Calculating on the basis of two moles of RDX from one mole of hexamine, that is about 65 % yield, ie. 1.65 moles of RDX from one mole of hexamine. I don't think you will get better than that.
There is obviously still a ways to go, so how about your AN? How have you dried it? Ammonium nitrate is notoriously difficult to dry since it tends to dissolve in its own moisture content when heated. One method is to heat it at ca. 70 C for 18-24 hours, then gradually increasing temp. Other protocols can also be used, the trend being low heat for a long time. If the AN seems to melt below about 165 C, it still contains water, and that will impact your yield of RDX.

BoroNar - 20-2-2026 at 01:25

Microtek

Thanks for replying, these times it is very hard to get into forum. I think this is the way "they" are trying to kill last place on internet where one can to study this matters, help others and share information...
I have dried AN but not at such extreme, used few times in ETN synth with perfect results. Will do that kind of drying process. Also, can vacuum chamber and silica gel dehydrate AN?
Here are my calculations for 1.65 molar ratio, still very bad result.

Hexamine input Grams 5
Hexamine input moles 0.0356668996904113 (5/140.186)

expected molar ratio X 1.65

RDX Expected moles 0.0588503844891787 (0.0356668996904113*1.65)
RDX Expected Grams 13.07 (0.0588503844891787*222.12)

RDX Received Grams 6.2
RDX Received moles 0.0279128399063569 (6.2/222.12)

RDX Mol. vs Hex Mol. 0.47

Still, I can’t find out what causes red fumes @65c. Will try very low speed temp increases, with 20-25min plateaus at every 10deg.

Microtek - 22-2-2026 at 00:44

I made a typo in my last post; 65 % yield is of course not 1.65 moles of RDX pr. mole of hexamine, but rather only 1.3 (since the expected molar ratio is 2:1). Your yield is 39 % which is a little low but not uncommon in an amateur setting.

Red fumes of NOx indicates either thermal decomposition of HNO3 (not likely at 65 C), reduction of HNO3 by compounds in the mix (likely) or decomposition of unstable nitration products (also likely).